As is well known, a circuit breaker is an automatically operated electro-mechanical device designed to protect a load from damage caused by a power overload or a short circuit. A circuit breaker may be tripped by an overload or short circuit causing an interruption of power to the load. A circuit breaker can be reset (either manually or automatically) to resume power flow to the loads. One type of circuit breaker that provides instantaneous short circuit protection to motors and/or motor control centers (“MCC”) is called a motor circuit protector (MCP). A typical MCP includes a temperature-triggered overload relay, a circuit breaker, and a contactor. An MCP circuit breaker must meet National Electric Code (“NEC”) requirements when installed as part of a UL-listed MCC to provide instantaneous overload protection.
Mechanical circuit breakers energize an electro-magnetic device such as a solenoid to trip a breaker instantaneously due to large surges in current such as by a short circuit. The solenoid is tripped when current exceeds a certain threshold. In order to provide protection over different types of motors, different MCP circuit breakers that match the operating parameters of the particular motor must be designed for each current rating. Each MCP circuit breaker is designed with specific trip point settings for a given current rating. MCPs must protect against fault currents while avoiding tripping on in-rush motor currents or locked-rotor currents, but these current levels vary by motor. Existing MCPs have a relatively limited operating range, so they are suitable for protecting motor circuits within the MCP's operating range. For motor circuits outside of a particular MCP's operating range, a different MCP must be designed for the operating parameters of those motor circuits.
It is costly to design a different MCP device for different current ratings, and it is also costly to inventory and distribute many different MCP devices. What is needed is an MCP device with user-adjustable and automatically configurable trip point settings over a broad range of current ratings. What is also needed is a circuit protection device that couples a mechanical adjustment button and a potentiometer for adjusting trip levels of an electrical circuit.